topic Re: Selecting elements of an array using property nodes in LabVIEW

Selecting elements of an array using property nodes

vlipje — Thu, 29 Aug 2002 15:05:57 GMT

I would like to know how I can access an array not by using the usual
'Index Array VI' but by using property nodes. I created an array with
a digital indicator and from this control a property node wich I set
to Selection size[], Selection start[] and Value (Selsize[],
selstart[], value). Changing the properties Selsize[] and selstart[]
does not result in a visible change of the active element and changing
the value property is not resulting in a change of the value of the
active element.

The reason of doing it this way is that I want to access elements of
array that is referenced by the controls[] property of another control
(cluster).

Johan

Re: Selecting elements of an array using property nodes

Labviewguru — Thu, 29 Aug 2002 15:58:49 GMT

Johan,

Not sure what you are doing, but in order to get array elements by using the properties of your cluster, I would suggest that you 'translate' the property of the cluster into the index of the array you are looking at, and retrieve the data that way.

Re: Selecting elements of an array using property nodes

storeyk — Fri, 30 Aug 2002 07:57:21 GMT

The Array element value returns the cell value which you select/click on. I tried to set key focus to the value i wanted, instead of manually clicking on the cell, but this didnt work. However, if you set the 'Index value', then you can change the Array element value, and as long as the array hasn't been clicked in, the active cell will be 0. See the attached example (in LV 6.0).

I also spent a little time looking at what the Selection start and Selection size do in the array property, and i couldn't work it out! It seemed to do nothing, and the help wasn't much use either. Maybe someone can enlighten us both here.

I hope this helps you..

Kim

Re: Selecting elements of an array using property nodes

vlipje — Fri, 30 Aug 2002 08:35:55 GMT

Labviewguru wrote in message news:<506500000005000000309B0000-1027480788000@exchange.ni.com>...
> Johan,
>
> Not sure what you are doing, but in order to get array elements by
> using the properties of your cluster, I would suggest that you
> 'translate' the property of the cluster into the index of the array
> you are looking at, and retrieve the data that way.

I've put a document with an example of the problem at:

http://uttnb71.tn.utwente.nl/asp/labview.doc

or

http://uttnb71.tn.utwente.nl/asp/labview.pdf

I hope it will make it clear what I want to do.

Johan

Re: Selecting elements of an array using property nodes

JeanPierre — Fri, 30 Aug 2002 10:31:07 GMT

Go to my LabVIEW page at http://cybertechs.qc.ca/~jpdrolet/labview and download the Cliked Array Element example. It shows how I used this feature to detect on which array element the user clicks. It also uses the selection feature. To see what Selection Start and Selection Size do, you must enable "Show Selection" in the advanced menu of the array. The selected elements are highlighted in blue.

Remember that property nodes purpose is mainly to manipulate controls appearance and behavior rather than data. You can read/write a control using the value property but it is not the preferred way and is less efficient.

Re: Selecting elements of an array using property nodes

Labviewguru — Fri, 30 Aug 2002 18:16:13 GMT

Johan,

I am clear as to what you want to do, but I am not sure why.

Is there a reason you just can't access the entire array from the reference, obtain the value (the entire array) and then index the element that you want?

Re: Selecting elements of an array using property nodes

vlipje — Sat, 31 Aug 2002 07:05:55 GMT

Labviewguru wrote in message news:<506500000005000000979B0000-1027480788000@exchange.ni.com>...
> Johan,
>
> I am clear as to what you want to do, but I am not sure why.
>
> Is there a reason you just can't access the entire array from the
> reference, obtain the value (the entire array) and then index the
> element that you want?

The bad thing is that the value you obtain is not an array but a
variant containing array data. You simply do not know what kind of
data is inside the array otherwise it could be strictly referenced

Johan

Re: Selecting elements of an array using property nodes

vlipje — Sat, 31 Aug 2002 10:05:55 GMT

"Jean-Pierre Drolet" wrote in message
news:506500000005000000729B0000-1027480788000@exchange.ni.com...
> Go to my LabVIEW page at http://cybertechs.qc.ca/~jpdrolet/labview and
> download the Cliked Array Element example. It shows how I used this
> feature to detect on which array element the user clicks. It also uses
> the selection feature. To see what Selection Start and Selection Size
> do, you must enable "Show Selection" in the advanced menu of the
> array. The selected elements are highlighted in blue.
>
> Remember that property nodes purpose is mainly to manipulate controls
> appearance and behavior rather than data. You can read/write a control
> using the value property but it is not the preferred way and is less
> efficient.

Je
an -Pierre,

I think I misunderstood the meaning of selection Start en selection size. I
thought it was way of making a particular element of an array active so that
you can read its value, but it appears not to be like that. With your
technique you can of course find out what the position of the element in the
array is and get its value with the arrayelement.value property but that is
only because you clicked on it. I want to read the value without clicking
the actual element.
Just plain giving a value to certain properties for selecting the element
and then reading its value.

Re: Selecting elements of an array using property nodes

JeanPierre — Sat, 31 Aug 2002 13:09:16 GMT

Johan,

if the variant array is your problem then you can take a look at the lvdata package of the OpenG Toolkit at http://sf.net/projects/opengtoolkit . It depends on the error package so download both lvdata and error packages.

The LabVIEW Data Tools contains numerous VIs to manipulate variant data. You can use "Index Array.vi" that inputs a variant array and an array of indices and outputs the array element (as a variant too). The toolset is still under active development so your feedback is appreciated for any feature that you would need and that is missing. While writing this I realize the the toolset lacks a "Replace Array Element.vi" for arrays...

On the other hand, if the array has always the same nuber o
f dimensions (1D, 2D,...) you can use the "To G Data" function to convert a variant array to an array of variant data. After the conversion you get an array of variants that you can manipulate like any other array to index and replace elements.

Re: Selecting elements of an array using property nodes

JeanPierre — Sat, 31 Aug 2002 16:11:56 GMT

Johan,

Here is a VI illustrating two ways to manipulate array data by reference. With both ways the whole array is read,modified and written back by value property. As you have seen, this is hardly done using the array element reference since it is a reference to a control not tied to a specific element but to the array element the user is currently editing.

Re: Selecting elements of an array using property nodes

Labviewguru — Sat, 31 Aug 2002 17:30:45 GMT

Johan,

It is interesting, but I just ran into what I think is a similar problem to yours, sort of...

I need to get ANY data from a cluster, and convert it to a string to write to a file. My program has no idea what the data is. It could be a string, a numeric, an array, whatever. Strings were of course no problem. Converting booleans was a little tricky, as was numerics. But now I have come across an array. The Variant returns something resembling the dimensions of the array. What I am planning to do is act upon this (I get a variant that contains "[nXn]" in it, so I can tell when it is an array) information to put the code into a mode where it can get the array data and then write it to a string.

This is going to be very difficult. What I wil
l more than likely do is just grab a reference to the array, and retrieve the value. Then, I can figure out the dimensions, and write the array as a single string, separated by commas, with the dimensions of the array at the start of the string.

As it has been suggested, this is probably how you should be going as well. The only way you can get to an element of an array is to get the array itself. Arrays in LabVIEW are stored as pointers, so trying to retrieve an element of an array through references seems impossible. Just grab the value of the reference "value" of the array, and index the array from there. I think your task is a lot easier than mine.

Also, if you go to LabVIEW help (not context help of course) from the "Variant to Data" function, you will see a link to an application note on Data Storage in LabVIEW that was included with your documentation. Read this document! It is extremely useful for what you are trying to do.

Re: Selecting elements of an array using property nodes

JeanPierre — Sat, 31 Aug 2002 20:16:59 GMT

Then again Labviewguru, take a look at the OpenG Toolkit packages! http://sf.net/projects/opengtoolkit
the lvdata package has VIs to manipulate variant data, the variantconfig has VIs to write clusters, arrays and variant data to INI files, and the string packages has a "Format Variant into String.vi".

Re: Selecting elements of an array using property nodes

storeyk — Mon, 02 Sep 2002 08:02:51 GMT

Johan, have you tried my example? It does let you read the value without clicking the actual element.

I have also updated it slightly (see below) to convert the variant data to a numeric (you stated in your post that your array was of digital indicators). As you know what your data will be there should be no problem converting from variant data.

The array has also been 'covered' with a decoration to stop it being clicked in, and the Index value is now a numeric, rather than an array.

I hope this makes things a little more clear for you. Let me know if this is not the case and i'll be glad to help some more.

Kim

Re: Selecting elements of an array using property nodes

JeanPierre — Mon, 02 Sep 2002 12:27:47 GMT

Johan,
it seems that you are using a news server that filters out messages with attachments. Some replies to your question (Kim and mine) do have VIs attached to show how you can achieve what you want.
The group comp.lang.labview is available on newsgroups.ni.com with attachments and also mirrored on NI Developpers Exchange forums. Your thread is shown at (remove line breaks):
http://exchange.ni.com/servlet/ProcessRequest?RHIVEID=101&RPAGEID=135&HOID=5065000000080000006E590000&USEARCHCONTEXT_CATEGORY_0=_49_%24_6_&USEARCHCONTEXT_CATEGORY_S=0&UCATEGORY_0=_49_%24_6_&UCATEGORY_S=0

Jean-Pierre

Re: Selecting elements of an array using property nodes

vlipje — Mon, 02 Sep 2002 12:36:02 GMT

Jean-Pierre,

This is very usefull, in fact this is what I am looking for the first
time.
Except for the arrays, I assume I have to insert the Index Array.vi
into the variant config package to write clusters to ini files.

I wanted to do a similar thing by breaking down a cluster in its
separate objects and then determining the value and name of each
individual object.
It looks like you can only access the seperate elements of an array
when it is converted to an variant.

Re: Selecting elements of an array using property nodes

vlipje — Mon, 02 Sep 2002 13:05:57 GMT

LabviewGuru,

I have read that document. It is indeed very useful, but I wanted to
avoid the use of variant data. It feels more clean to go down to the
elements by use of references. I will try to do the trick you are
explaning but think that I'm still ending up with variant data.
If it still doesn't work out the way I want I think I will use the
tools Jean-Pierre Drolet suggested for manipulating variant data. He
has a solution for the problem I wanted to tackle.

Thanks anyway up till now, because it was very usefull.

Re: Selecting elements of an array using property nodes

Mads — Mon, 02 Sep 2002 13:06:57 GMT

A bit off the topic, but - Open G had some useful functions, it was a bit of work to download and install though, it would be great if You made all the files available in one single download (could only find separate files for each function set, but maybe I was overlooking a bundle download). An installation set that put the tool as a top level "OpenG" button in the functions palette would also be great (regardless of the purpose of the installation...use or further development).

Re: Selecting elements of an array using property nodes

wiebe@CARYA — Mon, 02 Sep 2002 13:35:56 GMT

Johan,

Why not get the value (, the entire array, ) from the property node "value"?
Then you can use Array Subset to get the required array values.

This does what the example in the pdf file does. You can also replace the
elements, and write back to the "value" property.

Reading from and writing to SelStart/SelSize doesn't seem to work for arrays
(it does for strings). That is, I never got it to work... Anyway, I'm not
even able to select elements, so why bother reading the selection?

Regards,

Wiebe.

"Johan" wrote in message
news:9abf782f.0208290638.44566d93@posting.google.com...
> I would like to know how I can access an array not by using the usual
> 'Index Array VI' but by using property nodes. I created an array with
> a dig
ital indicator and from this control a property node wich I set
> to Selection size[], Selection start[] and Value (Selsize[],
> selstart[], value). Changing the properties Selsize[] and selstart[]
> does not result in a visible change of the active element and changing
> the value property is not resulting in a change of the value of the
> active element.
>
> The reason of doing it this way is that I want to access elements of
> array that is referenced by the controls[] property of another control
> (cluster).
>
> Johan

Re: Selecting elements of an array using property nodes

JeanPierre — Mon, 02 Sep 2002 22:59:22 GMT

Just a little patience Mads... OpenG Toolkit is still under active development. There will be tools like package manager that will download all the required components directly in your LabVIEW directory with palettes and Tools menu.
Stay tuned for more features, I just hope you enjoy the currently released VIs even if the installation is still a little quirky.

Re: Selecting elements of an array using property nodes

vlipje — Tue, 03 Sep 2002 07:49:29 GMT

Jean-Pierre, (from Johan now being Vlipje)

You still have a problem when the array is an array of clusters. Because of the variant it is impossible to get a reference to the actual cluster "elements".
I made a VI that makes clear where I want to go. I can resolve the elements of the inner cluster but can't access the individual values of of each control inside the inner cluster.

And this all has to be done without knowing what the actual structure of the cluster you want to read is.

Please look at the attached VI